Rectifier assemblies are often mounted on generators and should have high resistance to corrosion. These rectifiers also should reliably recover from short overloading conditions, have a minimum component count, be quickly and easily assembled either manually or with semi-automated production equipment, be economical to manufacture, and withstand mechanical stress with minimum sacrifice of thermo-conductivity. The rectifier assemblies should also provide an output current in a very direct manner, thus minimizing the number of interconnections.
Prior art rectifier assemblies have been designed with different needs in mind. In U.S. Pat. No. 4,606,000 to Steels et al.,embedded preformed leads are positioned in a wedge block configuration, and inserted in a dovetail receptacle that is extruded into an aluminum cooling member. It connects the polyphase stators leads to header sandwiched chip diodes by solder. It has become well known that these soldered connections will fatigue over time because of repeated thermal cycling. Short overloading conditions resulting in excessive diode heat will exceed the melting temperature of the solder, rendering the connection useless or, at the minimum, resulting in a high resistive connection exacerbating diode failure.
In U.S. Pat. No. 5,696,212 to DePetris, the key diode contact points are spring loaded with the assumption that the solder will melt and return to its original form. While this may prevent an immediate catastrophic failure, it is well known that the repeated melting and cooling of solder fatigues the metal, resulting in the formation of air bubbles with the familiar frosted appearance. This results in an increased contact resistance augmenting the gross diode-junction heat dissipation. This device also has a number of additional components, adding to the complexity of the design. In this patent, a solid phenolic gasket material has greater crush proof resistance, and contributes to a greater thermal resistance between the positive cooling member and the negative thermal conductive plate. Thus, this device requires a greater dependence on the forced air cooling requirements of the positive cooling member, resulting in additional isolated cooling fins and increased manufacturing costs.
In U.S. Pat. Nos. 4,646,838 and 5,812,388 to Keidar et al., a positive heat cooling member of a rectifier assembly is disclosed. Details of the type of diode used, how the diode is connected, and the thermo-conductive aspects of the rectifier are ignored. Keidar in U.S. Pat. No. 5,646,838 has added slots to the gasket contact area surface of the positive cooling member in an attempt to increase air flow under the cooling member. As the major direction of the air flow is perpendicular to these slots, only a minor difference in air pressure exists across these slots resulting in minimum air flow. Keidar's added slots to the positive cooling member lessens the thermo-conductivity area offsetting to a degree his claimed advantages of adding the slots.
U.S. Pat. No. 5,812,388, Keidar et al. embellishes said U.S. Pat. No. 5,646,838 by adding a serrated surface on a plan surface opposite to the gasket surface in the positive cooling member. It is well known in the art that any attempt to increase surface area of a forced air cooling member will aid in heat dissipation of the member. Keidar's placement of the serrated planar surface is positioned in such a manner to be perpendicular to the majority of air flow in the generator assembly, thus minimizing any advantageous effects. If the serrations were added to the through slots located between the fins of the cooling member or to the outer periphery of the cooling member, some benefit may be gained as the added area would be parallel to the majority of air flow in the generator configuration. The manufacturing cost of adding such serrations becomes highly debatable as to their cost effectiveness.
U.S. Pat. No. 4,606,000 to Steele, et al. shows a through hole in the positive cooling member for inserting a keyed battery bolt. The bolt contacts the cooling member via a retaining nut. An insulator and generator end-frame is compressed by tightening the nut. The path for current flow originating from the positive cooling member is via contact to the nut, then through the battery bolt. Further compression of the compressed insulator or thermal variations in the generator end frame can lead to the loosening of the nut resulting in a high resistive electrical connection.
U.S. Pat. No. 5,453,648 to Bradfield shows a threaded bolt with a corresponding threaded hole in the positive cooling member, while Bradfield effectively increases the bolt contact area to the positive cooling member. This was accomplished at the cost of eliminating the key locking feature of both the unshown insulator and the keyed hole in the generator end frame. A disadvantage of this method is that vibration or bumping on the battery cable can loosen the threaded bolt into the positive cooling member resulting both in an erratic connection and lack of compression on the positive-negative cooling member that depends on compression to assure electrical conductivity.
U.S. Pat. Nos. 4,952,829 and 5,331,231 to Armbruster et al. and Koplin et al., respectively, assigned to Robert Bosch GmBH, disclose rectifier devices for three-phase generators. These complicated rectifiers do not adequately disclose a good cooling mechanism as desired by intensive generator applications.